How to get the distance between two objects in the game engine?
You can use mathutils.Vector locations

import bge

scene = bge.logic.getCurrentScene()
# the object the sensor is connected to
owner = bge.logic.getCurrentController().owner
# the other object you want to get the distance to
obj2 = scene.objects['obj_name']
length = (owner.worldPosition - obj2.worldPosition).length

print(length)


This allows for easier manipulation, so for example if you only want to measure distance on a map (without taking altitude into account) you can do.

length = (owner.worldPosition.xy - obj2.worldPosition.xy).length